From 1978 to 1982, we enrolled and followed about 900 North Carolina children. We measured, among other things, PCBs and DDE in their mothers' breast milk, and followed the course of lactation. We found that women with higher DDE, but not PCB, levels weaned earlier, and we speculated that DDE?s estrogen activity might produce the effect. We later replicated the early weaning and DDE finding in Mexico. In 2001, more than a dozen countries in sub-Saharan Africa requested exemption from the world-wide ban on DDT in order to use it for malaria prevention. Using our data on weaning, as well as NIEHS/NICHD data on the relation between DDE and preterm birth, we estimated that the increase in infant mortality from spraying DDT was of the same order as the decrease from effective malaria control, and suggested that all infant deaths as well as time at weaning should be documented of DDT were to be used. We have also estimated the effect of breastfeeding on mortality in developed countries like the US, and find that even in the US breastfeed children have a substantially reduced mortality rate in the first year of life. Polychlorinated biphenyls (PCBs are among the most ubiquitous and persistent of environmental contaminants, and are detectable in most human beings worldwide. PCBs per se are toxic, teratogenic, and can cause impaired learning and behavioral abnormalities in laboratory animals. In children, transplacental exposure even at low, background levels may produce subtle psychomotor, cognitive, and memory impairment. In addition there have two mass poisonings by complex mixtures of heat-degraded PCBs. Two such exposures have occurred, one in Japan (Yusho) in 1968 and the other in Taiwan (Yucheng). With our colleagues in Taiwan, we have been following the 118 children born to Yucheng mothers, and reported in 2002 that they still had cognitive impairment and disordered behavior as 16 year olds, even if they had been born as long as 6 years after their mothers' exposure took place.We now have data on children born up to 13 years after the exposure, and hope to determine when, if ever, the mothers began to have unaffected children. DDT was banned in the US in 1972, and was proposed for a worldwide ban at the Stockholm Convention in 2001. However, countries in sub-Saharan Africa asked for exemptions, based on the resurgence in malaria and their need to use DDT for malaria control. Although their reasoning assumed no toxicity from DDT, we have shown that women with greater DDE exposure wean earlier, and our NIEHS/NICHD colleagues have shown that DDT exposure increases preterm births. Since both of these effects could increase infant mortality, we did a risk analysis to estimate the increase in infant deaths attributable to DDT exposure and the decrease attributable to DDT vector control.Because PCBs and DDT are carcinogens, their presence in breast milk creates a regulatory dilemma, in that authorities do not wish to recommend against breastfeeding but do not want to advocate the consumption of a contaminated food. We had previously done risk-risk analysis of breastfeeding in the presence of carcinogens, but found few data on the protection against mortality from breastfeeding in developed countries. This year we found a suitable data set with which to estimate the effect of breastfeeding on post-neonatal mortality in the US. The increase in infant mortality from early weaning and pre-term birth that would occur in sub-Saharan Africa from the use of DDT is of the same order of magnitude as the decrease resulting from extremely effective malaria control. In the US, breastfeeding is associated with a substantial reduction in the risk for post-neonatal mortality, and about 1200 deaths could be prevented or delayed if all children breastfed.